A touch sensor is known as an interface allowing a user to input information to a display device. The touch sensor is set on a screen of the display device, so that the user may operate an input button, an icon or the like displayed on the screen to easily input information to the display device. For example, Japanese Patent Application Publication No. 2009-244958 discloses an electronic device including a touch sensor provided in a Liquid Crystal display device.
In a conventional display device mounted with a touch sensor disclosed in Japanese Patent Laid-Open Patent Publication No. 2009-244958, a touch detection electrode is formed on the side of an opposing glass substrate. The opposing glass substrate is bonded to a transistor array substrate formed with a transistor. However, in a flexible display device in which a resin substrate is used for both the transistor array substrate and the opposing substrate, the opposing glass substrate is peeled off during the manufacturing process. Therefore, the touch detection electrode cannot be formed on the opposing substrate side. Furthermore, apart from a FPC which is connected to a driving circuit for driving a display panel, it was necessary to arrange another FPC connected to a touch detection driving circuit.